—How often do you clean your classroom?  —_________．

– Which of these two English books will you borrow? – I’ll borrow     of them. Because they are very interesting. 

 Lily and Grace are my best friends. ________ of them are very smart.

He is _______ clever boy that he can solve _____ many difficult problems.

Though I ______ the telephone number many times, the foreigner couldn’t write it down.